Sound-absorbing structures



I. A. NAMAN SOUND-ABSORBING STRUCTURES Dec. 8, 1959 2 Sheetsheet 1 FiledFeb. 25. 195'! INVENTOR.

ATTORNEY frrae/ A. Name/7 1959 1. A. NAMAN 2,916,101

SOUND-ABSORBING STRUCTURES Filed Feb. 25. 1957 2 Sheets-Sheet 2 /00 g maATTORNEY United States Patent SOUND-ABSORBING STRUCTURES Israel A.Naman, Houston, Tex. Application February 25, 1957, Serial No. 642,272

14 Claims. (Cl.181-42) This invention relates to sound-absorbingstructures. More particularly, the invention relates to structuresadapted to absorb or muflle sound normally accompanying the flow of afluid medium such as air or gas streams in a confined space.

The movement of streams of air through confining ducts or conduits, asis required in air-conditioning systems, is frequently accompanied byobjectionable sounds, elimination or muffling of which becomes highlydesirable. Many types of so-called sound traps or acoustic absorbershave heretofore been employed for that purpose but are ordinarily ofrelatively complicated and expensive construction, or may be relativelyineflicient sound absorbers, or cause undesirably high resistance to the'fluid stream flow so as to cause excessive pressure drop in the conduitsystems.

It is a primary object of this invention to provide an improvedsound-absorbing structure for installation in fluid stream ducts orconduits which is of relatively simple and low-cost construction, andwhich possesses a high degree of sound-absorbing efliciency withminimium resistance to the flow of the fluid stream therethrough.

An important object is the provision of a soundabsorbing cell or unit ofimproved specialized construction which is adapted to be incorporated inarrays or assemblies of different forms to provide sound-absorbingstructures of the character mentioned.

-A further object is the provision of a sound-absorbing structurecomprising a plurality of sound-absorbing cells disposed in an arrayhaving a shape and spacing relation of the cells adapted to effect highefliciency sound absorption with minimum pressure drop in the fluidstream.

An additional object is the provision of a sound-absorbing cell or unitcomprising, a hollow casing having acoustically'transparent side wallsand internally partitioned to define a plurality of sound-absorbingchambers of varying depth relative to the side walls adapted toattenuate different acoustic frequencies.

A more specific object is the provision of a soundabsorbing cell or unitcomprising, a generally rectangular hollow casing having spaced-apartacoustically transparent side Walls, the interior of the casing betweenthe side walls being divided transversely and longitudinally byintersecting acoustically. opaque partition members into a plurality ofchambers of varying depths relative to the side walls, said chambersbeing filled with acoustically absorbent material.

Still another object is theprovision of sound-absorbing cells of thekind described wherein the opposite ends of the casing are provided withcurved nose pieces and with tail pieces having convergent side walls,the angle of convergence of such side walls with respect to the longitudinal axis of the cell being in the range from about to about 25, andpreferably from about 12 to An additional object is the provision of asoundabsorbing structure comprising, an array of sound- 2,916,101Patented Dec. 8, 1959 absorbing units of the kind described arranged inlongitudinally spaced rows, the units of each row being transverselyspaced apart and in staggered relation to the units of the next adjacentrow whereby to prevent straight passage through the array.

A further object is the provision of a structure comprising an array ofsound-absorbing units of the kind described, each unit having a roundednose member and Y a tapered tail member, the array comprisinglongitudinally spaced rows of such units, the units of each row beingtransversely spaced apart and in staggered relation to the units of thenext adjacent row, the distance between the opposed surfaces of the noseand tail members of adjacent units being approximately half the distancebetween the units in each of said rows, whereby to providenon-straight-line flow through the array with minimum pressure drop.

Another object is to provide a sound-absorbing unit comprising agenerally rectangular hollow casing having spaced apart, parallelforaminous side walls, the interior of the casing being dividedtransversely and longitudinally by intersecting imperforate partitionmembers into two rows of chambers extending inwardly from each of theside walls, the longitudinal partition members being spaced at differingdistances from the side walls whereby to vary the depths of saidchambers in each of the rows relative to the side Walls.

Other and more specific objects and advantages of this invention willbecome more readily apparent from the following detailed descriptionwhen read in conjunction with the accompanying drawing which illustratesuseful embodiments in accordance with this invention,

In the drawing:

Fig. l is a perspective elevational view of a soundabsorbing cell orunit in accordance with this invention.

Fig. 2 is a fragmentary transverse sectional view taken generally alongline 22 of Fig. l;

Fig. 3 is a fragmentary vertical sectional view taken generally alongline 3-3 of Fig. 2; and

Figs. 4, 5 and 6 are generally schematic views illustrating severaldifferent arrays or assemblies of the soundabsorbing units which may beemployed to meet different conditions, the arrays being shown installedin conduits through which the fluid streams flow.

Referring first to Figs. 1, 2 and 3, which illustrate a sound-absorbingcell or unit in accordance with this invention, it will be seen that theunit comprises a generally rectangular casing, designated generally bythe numeral 10, defined by side walls 11-11 and top and bottom walls 12and 13, respectively. It will be understood that the top and bottomwalls 12 and 13 may be formed by the top and bottom walls of a conduitor duct in which the unit will ordinarily be installed, although, ifdesired, the unit may be made entirely self-contained by providing topand bottom walls 12 and 13 as shown. Side walls 11 are foraminous orotherwise acoustically transparent and may be constructed of sheet metalhaving perforations 14, or of expanded metal, wire mesh screen or thelike, as is well-known for use in structures of the kind hereincontemplated.

The interior of casing 10 is divided by a plurality of longitudinallyspaced, transverse partition members 15 which extend vertically from topto bottom of the casing and transversely from side wall to side wall ofthe casing. Longitudinally extending partition members 16 are arrangedbetween each pair of adjacent transverse partition members and extendvertically from top to bottom of the casing and are fastened along theirvertical edges to the adjacent partition members 15 in any suitablemanner, as by tack welding, or by means of screws, and the like.Partition members 15 and 16 are acoustically opaque and preferably areconstructed from thin imperforate sheet metal.

The arrangement of the intersecting transverse and longitudinalpartition members serves to divide the interior of casing into aplurality of chambers which extend inwardly from the respective sidewalls 11 and which communicate with the exterior of the unit through theopenings or perforations 14. The several longitudinal partition members16 are preferably positioned at different distances from the side wallsso as to vary the depths of the several chambers relative to the sidewalls. In the embodiment illustrated, the partition members 16 aredisposed at three different distances from each side wall, therebydefining the chambers A, B and C (Fig. 2) along one of the side Walls11, and the complementary chambers A B and C on the opposite sides ofthe partitions with respect to the other side wall 11. Thus there isprovided along each of the side walls 11, extending inwardly therefrom,a series of chambers of differing depths which will be adapted toattenuate sound waves of different frequencies, as is well understood.As shown, there may be several successive series of such chambersthroughout the length of the casing. All of the chambers are preferablysubstantially filled with a suitable acoustically absorbent material 17,such as fiber glass, rock wool, packed felt and the like.

Casing 10 may be provided at one end with a nose portion 18 defined by aconvex rounded end wall 19 which is likewise acoustically transparentand defines a chamber 18a which may be filled with the absorbentmaterial 17. At its opposite end, casing 10 may be fitted with a tailportion 20 defined by side wall portions 2121, which may be extensionsof side walls 1111. The side wall portions ll-21 converge at an angle tothe longitudinal axis of the unit, the angle of convergence relative tothe longitudinal axis being in the range of about 10 to 25 andpreferably from about 12 to 20. Wall portions 21 will also be foraminousor acoustically transparent and may be divided longitudinally by apartition member 16a into chambers 20a20a which may also be filled withthe acoustically absorbent material 17, as are the other chambersprovided in the interior of casing 10.

It will be understood that rounded nose portion 18 will ordinarily bethe upstream end of the unit, While tail portion 20 will be thedownstream end of the unit. It will also be understood that in somecases the use of the nose and tail portions may be dispensed with,particularly the tail portion, as will appear subsequently.

The sound-absorbing unit or cell heretofore described is a highlyefficient sound-absorbing device when placed in a fluid stream such asair or gas. which is accompanied by sound energy of differentfrequencies. The fluid passing over side walls 11, the unit ordinarilybeing installed parallel to the path of flow of the fluid, will, ofcourse, penetrate the side walls and the varying depths of the internalchambers and the acoustically absorbent material therein will beeffective to absorb different frequencies generally in accordance withthe depths of the several chambers.

The individual units of the kind described are very efficientsound-absorbing devices and are designed so that they may be installedin arrays of various forms in the ducts or conduits in which the fluidstreams flow to effectively absorb sound frequencies accompanying suchfluid. Figs. 4, 5 and 6 illustrate several different arrays which aresuitable.

Fig. 4 illustrates an array in which a plurality of units 10 arearranged in a rectangularly shaped duct or conduit D, such as areemployed in conventional air-conditioning systems, through which an airstream flows longitudinally in a direction indicated by the arrows. Inthe embodiment of Fig. 4 the units 10 are arranged in two transverserows R and R across the interior of the duct, it being understood theside walls of the units extend vertically from the bottom to the top ofthe duct and are suitably secured thereto. Downstream row R comprisesfour complete units and upstream row R contains three complete units, asshown, the units in one row being staggered transversely with respect tothose in the next adjacent row, the rows being longitudinally spacedwith respect to each other. The spacing between the units comprisingeach row will ordinarily be uniform and the same for both rows. Thestaggered arrangement of the rows is intended to prevent straightline-of-sight passage of fluid through the sound-absorbent structureformed by the array. This is to prevent the unimpeded passage of thehigh frequency sounds which would otherwise escape and to cause thefluid to traverse a zig-zag path through the array. To assure againstsuch unimpeded movement of the high frequency sounds, half units 10a maybe positioned in row R against each of the side walls of duct D in themanner shown. The units in both rows R and R will preferably be equippedwith the rounded nose portions 18, while those units in rows R will alsopreferably be equipped with tail portions 20 of the kind previouslydescribed. The longitudinal spacing between the rows, the angularity ofthe tail portions, and the spacing between the tail portions of row Rand the nose portions of rows R will be so selected that the clearanceor spacing be tween the opposing walls of the tail and nose portions ofthe adjacent rows, indicated by the dimension b, will be approximatelyone-half the spacing or distance between the units in each of the rows,indicated by the dimension a.

The angle of convergence of the wall portions forming the tail portions20 is selected to provide change in direction of flow of the fluidmedium suflicient to prevent unimpeded passage of high frequencies withminimum pressure drop. As noted previously, this angle is found to be ina range from 10 to 25 and preferably from about 12 to about 20. Wherethe array includes two rows of sound-absorbing units, as in Fig. 4, thetail portions on downstream row R may be dispensed with if desired andare, therefore, shown in broken lines in this illustration.

Fig. 5 illustrates another array employing one row R of units 10interspersed between two rows R of units 10, each row being of the formand arrangement previously described in connection with Fig. 4, and theunits 10 being identical with those previously described. This array maybe employed to secure a greater degree of sound reduction.

Fig. 6 illustrates a single row array useful in systems havingrelatively small sound reduction requirements. Under such conditions arow of three units 10 with or without the tail portions 20 (shown inbroken lines) may be sufficient to accomplish the results desired.

It will be understood that in large installations, more than one arraymay be installed. In some instances, several arrays may be installed atintervals in a single duct or fluid conduit. In any case, thesound-absorbing units herein described and the various arrays which maybe formed therewith will provide highly efficient sound reduction withminimum pressure drop in the fluid mediums passing therethrough.

While the invention herein described is particularly applicable toair-conditioning systems, it will be evident that it may be applied aswell to other acoustic systems, such as test stacks for engines,propellers, and the like.

It will be understood that various changes and modifications may be madein the details of the illustrative embodiments within the scope of theappended claims but without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. A sound-absorbing device for use in a fluid medium, comprising, agenerally rectangular casing having parallel spaced-apart foraminousside walls, and a pluarlity of intersecting transverse and longitudinalimperforate partition members positioned between said walls andrelatively arranged to divide the interior of the easing into aplurality of chambers of different depths relative to the side wallsadapted to attenuate different acoustic frequencies penetrating saidwalls.

2. A sound-absorbing device for use in a fluid medium, comprising, agenerally rectangular casing having parallel spaced-apart foraminousside walls, a plurality of intersecting transverse and longitudinalimperforate partition members positioned between said walls andrelatively arranged to divide the interior of the easing into aplurality of chambers of different depths relative to the side wallsadapted to attenuate different acoustic frequencies penetrating saidwalls, and acoustically absorbent material substantially filling said-chambers.'

3. A sound-absorbing device for use in a fluid medium, comprising, agenerally rectangular casing having parallel spaced-apart foraminousside walls, a plurality of intersecting transverse and longitudinalimperforate partition members positioned between said walls andrelatively arranged to divide the interior of the casing into aplurality of chambers of diflerent depths relative to the side wallsadapted to attenuate different acoustic frequencies penetrating saidwalls, said casing having a nose portion defined by a convexly curvedend wall and a tail portion defined by convergent side wall portions.

7 4. A sound-absorbing device according to claim 3 wherein the angle ofconvergence of said side wall portions relative to the longitudinal axisof said casing is in the range from about 10 to about 25.

5. A sound-absorbing device for use in a fluid medium, comprising, anelongate generally rectangular casing having parallel spaced-apartforaminous side walls, a plurality of intersecting transverse andlongitudinal imperforate partition members positioned between said wallsand relatively arranged to divide the interior of the casing into aplurality of chambers of different depths relative to the side wallsadapted to attenuate different acoustic frequencies penetrating saidwalls, said casing including a nose portion defined by a convexly curvedend wall and a tail portion defined by convergent side wall portions,and acoustically absorbent material substantially filling said chambers.

6. A sound-absorbing device according to claim 5 wherein the angle ofconvergence of said side wall portions relative to the longitudinal axisof said casing is in the range from about 10 to about 25.

7. In an acoustic system in which a fluid medium is adapted to flowlongitudinally through a confined space, a structure for absorbing soundenergy accompanying the flow of said medium, comprising, an array ofsoundabsorbing devices positioned in said confined space in the path offlow of said medium, said array comprising at least one transverse rowof said devices arranged in transversely spaced-apart relation acrosssaid space, each of said devices comprising, a generally rectangularcasing disposed parallel to the path of flow of said medium and havingparallel spaced-apart foraminous side walls extending vertically fromtop to bottom of said confined space, and a plurality of intersectingtransverse and longitudinal imperforate partition members positionedbetween said walls and relatively arranged to divide the interior of thecasing into a plurality of chambers of different depths relative to theside walls adapted to attenuate different acoustic frequenciespenetrating said side walls.

8. In an acoustic system inwhich a fluid medium is adapted to flowlongitudinally through a confined space, a structure for absorbing soundenergy accompanying the flow of said medium, comprising, an array ofsoundabsorbing devices positioned in said confined space in the path offlow of said medium, said array comprising at least one transverse rowof said devices arranged in transversely spaced-apart relation acrosssaid space, each of said devices comprising, a generally rectangularcasing disposed parallel to the path of flow of said medium and havingparallel spaced-apart foraminous side walls extending vertically fromtop to bottom of said confined space, a plurality of intersectingtransverse and longitudinal imperforate partition members positionedbetween said walls and relatively arranged to divide the interior of thecasing into a plurality of chambers of different depths relative to theside walls adapted to attenuate different acoustic frequenciespenetrating said side walls, and acoustically absorbent materialsubstantially filling said chambers.

9. In an acoustic system in which a fluid medium is adapted to flowlongitudinally through a confined space, a structure for absorbing soundenergy accompanying the flow of said medium, comprising, an array ofsoundabsorbing devices positioned in said confined space in the path offlow of said medium, said array comprising two or more longitudinallyspaced, transverse rows of said devices arranged in said space, thedevices in each row being transversely spaced-apart and the devices inone row being staggered relative to those in a next adjacent row, eachof said devices comprising, a generally rectangular casing disposedparallel to the path of flow of said medium and having parallelspaced-apart foraminous side walls extending vertically from top tobottom of said confined space, a plurality of intersecting transverseand longitudinal imperforate partition members positioned between saidwalls and relatively arranged to divide the interior of the casing intoa plurality of chambers of different depths relative to the side wallsadapted to attenuate different acoustic frequencies penetrating saidside walls, said casing having a nose portion defined by a convexlycurved end wall and a tail portion defined by convergent side wallportions, the relative spacing of the devices in said array being suchthat the spacing between the opposed walls of the nose and tail portionsof the devices in adjacent rows is approximately onehalf the spacingbetween adjacent devices in each of the rows.

10. In an acoustic system in which a fluid medium is adapted to flowlongitudinally through a confined space, a structure for absorbing soundenergy accompanying the flow of said medium, comprising, an array ofsoundabsorbing devices positioned in said confined space in the path offlow of said medium, said array comprising two or more longitudinallyspaced transverse rows of said devices arranged in said space, thedevices in each row being transversely spaced apart and the devices inone row being staggered relative to those in the next adjacent row, eachof said devices comprising, a generally rectangular casing disposedparallel to the path of flow of said medium and having parallelspaced-apart foraminous side walls extending vertically from top tobottom of said confined space, and a plurality of intersectingtransverse and longitudinal imperforate partition mem bers positionedbetween said walls and relatively arranged to divide the interior of theeasing into a plurality of chambers of different depths relative to theside walls adapted to attenuate different acoustic frequenciespenetrating said side walls, acoustically absorbent materialsubstantially filling said chambers, said casing having a nose portiondefined by a convexly curved end wall and a tail portion defined byconvergent side wall portions, the relative spacing of the device insaid array being such that the spacing between the opposed walls of thenose and tail portions of the devices in adjacent rows is approximatelyone-half the spacing between adjacent devices in each of the rows.

11. An array according to claim 10 wherein the angle of convergence ofsaid side wall portions of each of said devices relatives to thelongitudinal axis of the casings thereof is in the range from about 10to 25.

12. A sound-absorbing device for use in a fluid medium, comprising, anelongate generally rectangular casing having parallel spaced-apartforaminous side Walls, a plurality of longitudinally spaced imperforatepartition members extending transversely between the side walls and fromtop to bottom of the casing, a longitudinal imperforate partition memberextending between each pair of adjacent ones of the transverse partitionmembers and from top to bottom of said casing, the longitudinalpartition members being positioned at different distances from said sidewalls whereby to define with the transverse partition members aplurality of chambers of different depths relative to the side wallsadapted to attenuate dilferent acoustic frequencies penetrating the sidewalls.

13. A sound-absorbing device according to claim 12 wherein said chambersare substantially filled with acoustically absorbent material.

14. In an acoustic system in which a fluid medium is adapted to flowlongitudinally through a confined space, a structure for absorbing soundenergy accompanying the flow of said medium, comprising, an array ofsoundabsorbing devices positioned in said confined space in the path offlow of said medium, said array comprising two or more longitudinallyspaced transverse rows of said devices arranged in said space, thedevices in each row being transversely spaced-apart and the devices inone row being staggered relative to those in the next adjacent row, eachof said devices, comprising, an elongate generally rectangular casingdisposed parallel to the path of flow of said medium and having parallelspaced-apart foraminous side walls extending from top to bottom of saidconfined space, a plurality of longitudinally spaced imperforatepartition members extending transversely between said side walls andfrom top to bottom of said casing, a longitudinal imperforate partitionmember extending between each pair of adjacent ones of the transversepartition members and from top to bottom of said casing, thelongitudinal partition members being positioned at different distancesfrom said side walls whereby to define with the transverse partitionmembers a plurality of chambers of different depths relative to the sidewalls adapted to attenuate difierent acoustic frequencies penetratingthe side walls, and acoustically absorbent material substantiallyfilling said chambers.

References Cited in the file of this patent UNITED STATES PATENTS2,075,263 Bourne Mar. 30, 1937 2,350,513 Leadbetter June 6, 19442,519,162 Tucker Aug. 15, 1950 2,759,554 Baruch Aug. 21, 1956 FOREIGNPATENTS 733,329 Great Britain July 6, 1955

